1. Field of the Invention
The present invention relates to a duplex unit that reverses a sheet to form images at both sides of the sheet, for use in an image forming apparatus such as a copying machine, a facsimile, a printer, or the like.
2. Discussion of the Background
As illustrated in FIG. 12, in a background image forming apparatus for forming images on both sides of a sheet, a reverse unit 101 for reversing a sheet is provided at a side (right side as viewed in FIG. 12) of a main body case 102. The reverse unit 101 is rotatably provided around a first supporting shaft (not shown) which is provided at a lower part of the reverse unit 101 in the direction separating from the main body case 102. Below the reverse unit 101, a manual sheet feeding tray 103 that manually feeds a sheet is rotatably provided around a second supporting shaft 104 which is provided in a manual sheet feeding unit 117 in the direction separating from the main body case 102.
The main body case 102 houses sheet feeding trays 105, a sheet transfer path 109, an image forming unit 107, a fixing unit 108, and a sheet stacker unit 106. The sheet transfer path 109 is formed in the main body case 102 such that a sheet is conveyed from the sheet feeding tray 105 or the manual sheet feeding tray 103 to the sheet stacker unit 106 via the image forming unit 107 and the fixing unit 108.
In a case 110 of the reverse unit 101, a reverse path 111 and a refeed path 112 that is separated from the reverse path 111 are formed. At a separation point between the reverse path 111 and the refeed path 112, a reverse roller 113 is provided. The reverse roller 113 is reversible and conveys the sheet that is guided in the reverse path 111 to the refeed path 112 in a switchback direction. A one end of the reverse path 111 connects to the sheet transfer path 109 in the main body case 102 and the other end connects to an opening 114 that is provided at the right-hand side of the case 110 in FIG. 12 and opens outward. The opening 114 is closed by a sheet reverse guide plate 115. The sheet reverse guide plate 115 is rotatably supported around a supporting shaft 116 provided at the reverse unit 101 in the direction separating from the reverse unit 101.
In the above-described image forming apparatus with the reverse unit 101 and the manual sheet feeding unit 117, an image is formed on a sheet fed from the sheet feeding tray 105 or the manual sheet feeding tray 103 at the image forming unit 107 during the sheet passes through the sheet transfer path 109. The sheet having the image is discharged to the sheet stacker unit 106.
When images are formed on both sides of a sheet, the sheet having an image on one side is guided to the reverse path 111. When the trailing edge of the sheet passes the separation point between the reverse 111 and the refeed path 112, the reverse roller 113 is switched to rotate in the switchback direction (i.e., in the direction toward the refeed path 112), and the sheet is conveyed to the refeed path 112. The sheet is then conveyed to the sheet transfer path 109 again from the sheet refeed path 112 so as to have an image on the backside of the sheet in the image forming unit 107, and is discharged to the sheet stacker unit 106.
In the background image forming apparatus with the above-described configuration in FIG. 12, because the manual sheet feeding tray 103 is installed outside of the case 110 of the reverse unit 101 and is protruded from the case 110, people passing by the image forming apparatus may accidentally contact and break the manual sheet feeding tray 103. In addition, when an operator moves the image forming apparatus, the manual sheet feeding tray 103 may be opened due to vibration. As a result, the manual sheet feeding tray 103 may be broken by striking against surrounding items.
When a sheet is jammed in the sheet transfer path 109, an operator makes an operation space for removing the jammed sheet by rotating the reverse unit 101 around the first supporting shaft in the direction separating from the main body case 102. The operator reaches a hand into the space with the jammed sheet.
When the operator opens the reverse unit 101 for removing the jammed sheet in the sheet transfer path 109, the manual sheet feeding tray 103 needs to be opened first, and then the reverse unit 101 can be opened. On the other hand, when the operator closes the reverse unit 101 after removing the jammed sheet, the reverse unit 101 is closed first, and then the manual sheet feeding tray 103 needs to be closed. In other words, the operator needs to open and close not only the reverse unit 101 but also the manual sheet feeding tray 103 to remove the jammed sheet (i.e., the operator needs to perform two steps). The operator is therefore unnecessarily inconvenienced by opening and closing the reverse unit 101 and the manual sheet feeding tray 103 when the operator removes a jammed sheet.
Further, when a sheet having a length in the sheet conveying direction longer than the length of the reverse path 111 between the reverse roller 113 and the opening 114 (hereinafter referred to as a large size sheet) is reversed in the reverse unit 101, an operator needs to open the opening 114 by rotating the sheet reverse guide plate 115 around the supporting shaft 116 to protrude the leading edge of the large size sheet from the case 110. The open condition of the sheet reverse guide plate 115 is indicated by a dotted line in FIG. 12. In addition, when the manual sheet feeding tray 103 is closed, the operator needs to open the manual sheet feeding tray 103 first, and then rotate the sheet reverse guide plate 115 to protrude the leading edge of the large size sheet from the case 110.
Furthermore, when the operator uses an image forming apparatus installed at a place apart from an operator by a remote operation and when a large size sheet is reversed in the reverse unit 101, the operator needs to go to the image forming apparatus to rotate the sheet reverse guide plate 115 around the supporting shaft 116 and open the opening 114. Opening the sheet reverse guide plate 115 every time a large sized sheet is reversed in the reverse unit 101 becomes a burden on the operator. If an additional device for opening the sheet reverse guide plate 115 by a remote operation is installed to the image forming apparatus, an installation space and a number of construction parts increase in the image forming apparatus.